Superconducting Solenoids for COMET KEK Cryogenics Center, Osaka Univ. Kuno-san’s Team, J-PARC MLF Muon Group

Layout of Beam Line Magnets Pion Capture – High Field – High Radiation Transport & Decay – Medium Field – Curved solenoid Experiment – Low Field – Large volume – Curved solenoid

Pion Capture Solenoid Requirement High Field – More pion to capture – More (better) conductor – Larger stored energy High Radiation – High Power Beam – Heat Load – Radiation Damage

Big SC Solenoids in Real World Heat Load ~1W Cost ~1M$ Heat Load ~10kW Cost ~100M$ MRI Magnets Field: 1~4T Cooling: He Free? Detector Solenoids Field: 1~4T (NbTi) Cooling: Indirect Al Stabilized Cable With Cooling pipes Fusion (ITER CS model) Field: ~13T (Nb3Sn) Cooling: Direct Cable in Conduit Heat Load ~100W Cost ~10M$

Technology Choice Conductor Material 1.NbTi (~5T) choice for now 1.Well established 2.Not Expensive 2.Nb3Sn or Nb3Al (~12T) 1.Established for solenoids 2.Expensive (x5:conductor, x2:assebly to NbTi) 3.High Tc (~20T??) 1.Not established for high field magnets 2.Very expensive

Technology Choice Heat Load 50GeV x 15  A – Beam: 750kW – Coil: ~100W – Cable in Conduit? 8GeV x 7  A – Beam: 56kW – Coil: ~10W – Detector Solenoid

Mostly Common Feature Aluminum stabilized cable quench stability quench protection transparency Indirect cooling with cooling pipe 2 phase forced flow Thermo siphon Technology well established Many solenoids are in use Familiar to people in high energy physics Good for field up to ~5T 4T already achieved Good Solution for near future plan With modest budget Detector Solenoids

ATLASMEC B 0 [T]256 Bpeak [T] I [A] CoilLayer124 Rinn [mm] Length [mm] Support-Cyl [mm]1210 ConductorWidth [mm]4.25 (4.5)4.7 (5) Hight [mm]30 J cond [A/mm 2 ] StrandDiameter [mm]1.28 Number32 Total CrossSection41.1 NbTi/Cu/Al1/1.1/5.0 J NbTi [A/mm 2 ] LoadLineRatio Bc [T] Jc [A/mm 2 ] GeneralM [ton] E [MJ] E/M [kJ/kg] σh [MPa] σeq [MPa] σeq/σ Capture Solenoid Design 5mm 30mm

Temperature Margin Indirect cooling Cooling path from conductor to cooling pipe i.e. Temp. gradient We choose 5T version More temp margin 2 < 4 layer (transparency) Lower peak field

Quench Protection M-E conversion Quench Stored energy partly extracted partly into coil To protect coil spread heat evenly Still there are limit Parameter to look Stored Energy to Coil Mass Ratio

Yield Strength VS RRR Good RRR: for quench stability and protection High Yield Strength: for high EM force

High Yield Strength Al stabilized Conductor R&D For High Energy Physics – Higher Field ： > 5 Tesla – Larger Size ： Diameter 〜 10m Combination of Various Technology – ATLAS Al Ni Alloy Ni-0.5 ~ 1 % – CMS-Hybrid Support A >> A7020 Y.S.(0.2%) = 400 MPa RRR = ~ 400

13 An R&D Work using ATLAS-CS Conductor + A6061-T6 T.S. is > 50 % reinforced with A6061 using Electron Beam, and Laser Beam Welding LBW may be a potential technology EBW, LBW Laser Beam Welding

Refrigerator Cryocoolers (GM or pulse tube) may not be strong enough Maybe Helium refrigerator plant needed

Guideline for magnet design Optimize the magnetic field design below 6 T – As base-line, using NbTi superconductor (with a future option for > 10 T Nb3Sn, Nb3Al magnet for the pion capture solenoid) Apply “thin solenoid” design concept with Al- stabilized superconductor and indirect-cooling to – Minimize radiation heating, – Refer technology established at, ATLAS, BESS, and CMS Solenoid

Toward Higher Field Al-stabilized Nb3Sn/Nb3Al Solenoid beyond 10 T An R&D may be proposed in cooperation with NIFS.

Toward Higher Beam Power Cable in conduit – Removal of large heat load – ITER CS Experienced by model Nb 3 Sn ready Up to 13 T Can be ideal If affordable… ITER CS: 170M€

Capture Solenoid Summary & Issues For Pion Capture Solenoid for J-PARC – Detector Solenoid Technologies can be good solution Field ~5T, Heat Load ~10W (Beam Power ~56kW) – More advanced technologies are also available with some more money… Issues – High Radiation Doze Insulation material: Organic < 10 7 Gy – High Neutron Fluence Al and Cu: Resistivity change Superconductor: Jc change

What about others Pion Capture – High Field – High Radiation Transport & Decay – Medium Field – Curved solenoid Experiment – Low Field – Large volume – Curved solenoid

Transport solenoid COMET is not the only project needing muon transport solenoid Even in J-PARC there is a similar curved solenoid needed – J-PARC MLF muon beam line – Lot of similarity in spec – Joint R&D Osaka Univ KEK muon group KEK cryogenics center

J-PARC Muon Beam Line Field; ~2T Aparture; ~0.4 m Limited Access to shielded area – Refrigerator must be outside of shield – Limited Space for the refrigerators – Long distance to cold head to coil front – Conduction Cooling with Higher Temperature

Trial Winding of Curved Section with MgB2 conductor Purchase two kinds of MgB2 conductor from Columbus SC – 1 is the 1.13 mm diameter round wire Will be wound by a company – 2 is the 1.5 * 2.5 mm square wire Will be wound by Nakahara and Adachi at KEK They will be wound this winter and Tested in next spring R&D Coil made at KEK in house NbTi Already wound Test just started

R&D on Transport SC Solenoid Coil by company will be wound till Mar. R&D on trim dipole coil

Trial Winding of Curved Section with MgB2 conductor Purchase two kinds of MgB2 conductor from Columbus SC – 1 is the 1.13 mm diameter round wire Will be wound by a company – 2 is the 1.5 * 2.5 mm square wire Will be wound by Nakahara and Adachi at KEK They will be wound this winter and Tested in next spring

MgB2 conductor actually purchasing Monel 400 sheathed Diameter: 1.13mm Composition MgB 2 (Vol %)14.6 Fe (Vol %)10.8 Cu (Vol %)13.8 Ni (Vol %)15.8 Monel 400 (Vol %)45.0 Monel 400 sheathed Diameter: 1.13mm Composition MgB 2 (Vol %)14.6 Fe (Vol %)10.8 Cu (Vol %)13.8 Ni (Vol %)15.8 Monel 400 (Vol %)45.0 Cost: 3€/m There is also 1.5 mm * 2.5 mm conductor

Themal Conductivity and Specific Heat of Cu and Al NbTiMgB2 Thermal Conductivity: ~ 3 times better Cp: about 10 times larger

Refrigerator Performance Refrigerator Efficiency – Improve significantly at higher temperature 7.2 kW

Transport Solenoid Summary MgB2 can be a good candidate – Operation Temperature 10~20 K – Better Refrigerator Performance – Best Thermal Conductivity – Better Specific Heat – Good Cost saving solution